Apparatus and methods for vco linearization

Abstract

A method of linearizing a frequency versus tuning voltage response of a voltage controlled oscillator comprising multiple varactor sets. In one example, a the method of linearizing includes acts of providing a first varactor set with a first bias voltage, providing a second varactor set with a second bias voltage, and adjusting the first and second bias voltages so as to linearize the frequency versus tuning voltage response of the voltage controlled oscillator over a selected operating frequency range of the voltage controlled oscillator. The method can be extended to N varactor sets and can be applied to many RF CMOS or analog CMOS components, including voltage controlled oscillators.

1 . A tunable voltage controlled oscillator comprising:
 a first varactor set comprising at least one CMOS varactor;   a second varactor set comprising at least one CMOS varactor and coupled in parallel with the first varactor set;   a first bias voltage applied to the first varactor set; and   a second bias voltage applied to the second varactor set;   wherein the first and second bias voltages are selected such that a frequency versus tuning voltage of the voltage controlled oscillator is substantially linear over a selected operating frequency range of the voltage controlled oscillator.   
   
   
       2 . The tunable voltage controlled oscillator as claimed in  claim 1 , wherein the CMOS varactors are accumulation mode MOS capacitors. 
   
   
       3 . The tunable voltage controlled oscillator as claimed in  claim 1 , wherein the CMOS varactors are depletion mode MOS capacitors. 
   
   
       4 . The tunable voltage controlled oscillator as claimed in  claim 1 , wherein the CMOS varactors are reverse-biased pn-junction diodes. 
   
   
       5 . The tunable voltage controlled oscillator as claimed in  claim 1 , further comprising a third varactor set and a third bias voltage applied to the third varactor set; and wherein the first, second and third bias voltages are selected such that the frequency versus tuning voltage of the voltage controlled oscillator is substantially linear over the selected operating frequency range of the voltage controlled oscillator. 
   
   
       6 . A method of linearizing a frequency versus tuning voltage response of a voltage controlled oscillator comprising a first varactor set and a second varactor set, the method comprising acts of:
 providing the first varactor set with a first bias voltage;   providing the second varactor set with a second bias voltage; and   adjusting the first and second bias voltages so as to linearize the frequency versus tuning voltage response of the voltage controlled oscillator over a selected operating frequency range of the voltage controlled oscillator.   
   
   
       7 . The method as claimed in  claim 6 , further comprising an act of providing the first and second varactor sets with a common tuning voltage. 
   
   
       8 . The method as claimed in  claim 6 , wherein the voltage controlled oscillator further includes a third varactor set, and further comprising providing a third bias voltage to the third varactor set;
 wherein the act of adjusting includes adjusting the first, second and third bias voltages so as to linearize the frequency versus tuning voltage of the voltage controlled oscillator over the selected operating frequency range of the voltage controlled oscillator.   
   
   
       9 . The method as claimed in  claim 8 , wherein the act of adjusting includes adjusting the first, second and third bias voltages such that the frequency versus tuning voltage response of the voltage controlled oscillator is substantially linear over the selected operating frequency range of the voltage controlled oscillator. 
   
   
       10 . A voltage controlled oscillator comprising:
 a tunable resonant circuit including at least one inductor, a first set of varactors and a second set of varactors, the first and second sets of varactors being connected in parallel with one another;   a tuning port constructed and arranged to receive a tuning voltage;   a first port coupled to the first varactor set and constructed and arranged to receive a first bias voltage; and   a second port coupled to the second varactor set and constructed and arranged to receive a second bias voltage;   wherein the first and second bias voltages are selected such that an operating frequency of the voltage controlled oscillator changes in a substantially linear manner in response to changes in the tuning voltage.   
   
   
       11 . The voltage controlled oscillator as claimed in  claim 10 , wherein the first set of varactors includes at least one CMOS accumulation mode or depletion mode capacitor; and wherein the second set of varactors includes at least one CMOS accumulation mode or depletion mode capacitor.